1. Field of the Invention
This invention relates to a vacuum pump having an exhaust portion formed by rotating blade portions and stationary blade portions.
2. Description of the Related Art
In a vacuum pump such as a turbo-molecular pump, a rotor having rotating blade portions arranged in multiple stages is rotated at high speed in a pump container formed by a casing member and a base member, and a gas molecule is moved from the intake port side to the exhaust port side by the rotating blade portions and stationary blade portions arranged between the stages of the rotating blade portions.
Each stage of the rotating blade portions has rotor blades, and each stage of the stationary blade portions has stator blades. The stationary blade portions are supported at predetermined intervals by spacers arranged on the outer circumferential side of the stationary blade portions. The stationary blade portions are formed into one ring shape by combining a pair of halved ring shape members. That is, one ring is formed by abutting two side end surfaces each other in the radial direction of the halved ring shape members. The rotor blades and the stator blades are formed so as to be inclined with respect to a rotation surface of the rotor. Gaps of predetermined dimension are provided between the rotor blades and the stator blades.
As a method of manufacturing the stationary blade portions, there are a method of forming by mechanical working and a method of forming by plastic working. The method of manufacturing by the plastic working is advantageous in terms of cost.
In the method of forming by the plastic working, a plurality of stator blades formed by pressing a plate and arranged at a predetermined inclination angle along the circumferential direction is coupled by an inner circumferential rim serving as an inner circumferential edge and an outer circumferential rim serving as an outer circumferential edge, so that a stationary blade portion is manufactured (for example, refer to JP 2008-144694 A).
Due to variation at the time of the working, in the stationary blade portion supported by spacers, the side of the inner circumferential rim is displaced in the axial direction of a rotor with respect to the side of the outer circumferential rim. By this displacement, a risk that the stationary blade portions are brought into contact into the rotating blade portions is generated.